U.S. patent number 10,634,751 [Application Number 15/721,840] was granted by the patent office on 2020-04-28 for systems and methods for reducing artifacts in mri images.
This patent grant is currently assigned to UIH AMERICA, INC.. The grantee listed for this patent is UIH AMERICA, INC.. Invention is credited to Yu Ding, Jinbo Ma, Zhenhua Shen, Qing Wei, Yuan Zheng.
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United States Patent |
10,634,751 |
Zheng , et al. |
April 28, 2020 |
Systems and methods for reducing artifacts in MRI images
Abstract
A method for modifying RF pulse infidelity is provided. The
method may include obtaining a designed time-domain waveform. The
method may also include directing a radio frequency power amplifier
(RFPA) of a magnetic resonance imaging (MRI) scanner to generate an
output RF pulse based on the designed time-domain waveform. The
method may also include measuring an output time-domain waveform of
the output RF pulse. The method may also include determining, based
on the designed time-domain waveform and the output time-domain
waveform, a modified time-domain waveform corresponding to an
excitation RF pulse. The method may also include directing the MRI
scanner to generate, using a waveform generator and the RFPA and
based on the modified time-domain waveform, the excitation RF pulse
to excite one or more slices of an object in an MRI scan.
Inventors: |
Zheng; Yuan (Houston, TX),
Ma; Jinbo (Shanghai, CN), Ding; Yu (Houston,
TX), Wei; Qing (Shanghai, CN), Shen; Zhenhua
(Shanghai, CN) |
Applicant: |
Name |
City |
State |
Country |
Type |
UIH AMERICA, INC. |
Houston |
TX |
US |
|
|
Assignee: |
UIH AMERICA, INC. (Houston,
TX)
|
Family
ID: |
65403235 |
Appl.
No.: |
15/721,840 |
Filed: |
September 30, 2017 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20190101608 A1 |
Apr 4, 2019 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01R
33/3614 (20130101); G01R 33/4833 (20130101); G01R
33/4835 (20130101); G01R 33/5659 (20130101); G01R
33/5617 (20130101); G01R 33/543 (20130101); G01R
33/3607 (20130101) |
Current International
Class: |
G01R
33/561 (20060101); G01R 33/54 (20060101); G01R
33/483 (20060101); G01R 33/565 (20060101); G01R
33/36 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
M Barth et al. Simultaneous multislice (SMS) imaging techniques,
Magnetic Resonance in Medicine, 2016, 19 pages. cited by
applicant.
|
Primary Examiner: Rodriguez; Douglas X
Attorney, Agent or Firm: METIS IP LLC
Claims
What is claimed is:
1. A system, comprising: one or more storage devices storing a set
of instructions; and one or more processors configured to
communicate with the storage device, wherein when executing the set
of instructions, the system is caused to: obtain a designed
time-domain waveform wherein the designed time-domain waveform is a
scanning sequence; direct a radio frequency power amplifier (RFPA)
of a magnetic resonance imaging (MRI) scanner to generate an output
RF pulse based on the designed time-domain waveform; measure an
output time-domain waveform of the output RF pulse; determine,
based on the designed time-domain waveform and the output
time-domain waveform, a modified time-domain waveform corresponding
to an excitation RF pulse wherein the modified time-domain waveform
including a compensation time-domain waveform; and direct the MRI
scanner to generate, using a waveform generator and the RFPA and
based on the modified time-domain waveform, the excitation RF pulse
to excite one or more slices of an object in an MRI scan; wherein
to determine the modified time-domain waveform corresponding to the
excitation RF pulse based on the designed time-domain waveform and
the output time-domain waveform, the system is caused to: transform
the designed time-domain waveform into a designed frequency-domain
waveform with one or more excitation bands; transform the output
time-domain waveform into the output frequency-domain waveform;
determine the one or more frequency-domain sidebands in the output
frequency-domain waveform by comparing the designed
frequency-domain waveform with the output frequency-domain
waveform; select a portion of the output frequency-domain waveform,
the portion of the output frequency-domain waveform including the
one or more frequency-domain sidebands but not the one or more
excitation bands; determine a compensation frequency-domain
waveform based on the selected portion of the output
frequency-domain waveform; transform the compensation
frequency-domain waveform into a compensation time-domain waveform;
and determine the modified time-domain waveform based on the
compensation time-domain waveform and the designed time-domain
waveform.
2. The system of claim 1, wherein the modified time-domain waveform
is closer to satisfying an execution capability criterion than the
designed time-domain waveform, the execution capability criterion
embodying a criterion for a refocusing flip angle of the designed
RF pulse.
3. The system of claim 1, wherein a phase difference between the
selected portion of the output frequency-domain waveform and the
compensation frequency-domain waveform is 180.degree..
4. The system of claim 1, wherein to determine the modified
time-domain waveform corresponding to the excitation RF pulse, the
system is caused to: repeatedly determine an updated time-domain
waveform in an iteration process including a plurality of
successive iterations until a termination criterion is satisfied,
wherein the updated time-domain waveform determined at the end of
the iteration process is the modified time-domain waveform.
5. The system of claim 4, at least one of the plurality of
iterations including: determining the updated time-domain waveform
based on the designed time-domain waveform and a previous output
time-domain waveform, the previous time-domain waveform
corresponding to the designed time-domain waveform in a first
iteration of the iteration process or a previously updated
time-domain waveform determined in a previous iteration, the
updated time-domain waveform corresponding to an updated RF pulse;
directing the RFPA of the MRI scanner to generate the updated RF
pulse; and measuring an output time-domain waveform of the updated
RF pulse.
6. The system of claim 5, wherein at feast one of the plurality of
iterations further includes: determining an iteration count of
iterations that have been performed; determining that the iteration
count is equal to or greater than a first threshold; and
terminating, based on the determination that the iteration count is
equal to or greater than the first threshold, the iteration
process.
7. The system of claim 5, wherein at least one of the plurality of
iterations further includes: displaying, to a user, a
frequency-domain waveform of an RF pulse generated by the RFPA
based on the modified time-domain waveform updated in the at least
one of the plurality of iterations; receiving, from the user, an
instruction related to the updated time-domain waveform determined
in the at least one of the plurality of iterations; and
terminating, based on the received instruction, the iteration
process.
8. The system of claim 7, wherein the received instruction includes
that the updated RF pulse generated by the RFPA based on the
updated time-domain waveform generated in the at least one of the
plurality of iterations is acceptable.
9. A method implemented on a computing device having one or more
processors and one or more storage devices, the method comprising:
obtaining a designed time-domain waveform wherein the designed
time-domain waveform is a scanning sequence; directing a radio
frequency power amplifier (RFPA) of a magnetic resonance imaging
(MRI) scanner to generate an output RF pulse based on the designed
time-domain waveform; measuring an output time-domain waveform of
the output RF pulse; determining, based on the designed time-domain
waveform and the output time-domain waveform, a modified
time-domain waveform corresponding to an excitation RF pulse
wherein the modified time-domain waveform including a compensation
time-domain waveform; and directing the MRI scanner to generate,
using a waveform generator and the RFPA and based on the modified
time-domain waveform, the excitation RF pulse to excite one or more
slices of an object in an MRI scan; wherein determining the
modified time-domain waveform corresponding to the excitation RF
pulse based on the designed time-domain waveform and the output
time-domain waveform comprises: transforming the designed
time-domain waveform into a designed frequency-domain waveform with
one or more excitation bands; transforming the output time-domain
waveform into an output frequency-domain waveform; determining one
or more frequency-domain sidebands in the output frequency-domain
waveform by comparing the designed frequency-domain waveform with
the output frequency-domain waveform; selecting a portion of the
output frequency-domain waveform, the portion of the output
frequency-domain waveform including the one or more
frequency-domain sidebands but not the one or more excitation
bands; determining a compensation frequency-domain waveform based
on the selected portion of the output frequency-domain waveform;
transforming the compensation frequency-domain waveform into a
compensation time-domain waveform; and determining the modified
time-domain waveform based on the compensation time-domain waveform
and the designed time-domain waveform.
10. The method of claim 9, wherein the modified time-domain
waveform is closer to satisfying an execution capability criterion
than the designed time-domain waveform, the execution capability
criterion embodying a criterion for a refocusing flip angle of the
designed RF pulse.
11. The method of claim 9, wherein a phase difference between the
selected portion of the output frequency-domain waveform and the
compensation frequency-domain waveform is 180.degree..
12. The method of claim 9, wherein determining the modified
time-domain waveform corresponding to the excitation RF pulse
comprises: repeatedly determine an updated time-domain waveform in
an iteration process including a plurality of successive iterations
until a termination criterion is satisfied, wherein the updated
time-domain waveform determined at the end of the iteration process
is the modified time-domain waveform.
13. The method of claim 12, at least one of the plurality of
iterations including: determining the updated time-domain waveform
based on the designed time-domain waveform and a previous output
time-domain waveform, the previous output time-domain waveform
corresponding to the designed time-domain waveform in a first
iteration of the iteration process or a previously updated
time-domain waveform determined in a previous iteration, the
updated time-domain waveform corresponding to an updated RF pulse;
directing the RFPA of the MRI scanner to generate the updated RF
pulse; and measuring an output time-domain waveform of the updated
RF pulse.
14. The method of claim 13, wherein at least one of the plurality
of iterations further includes: determining an iteration count of
iterations that have been performed; determining that the iteration
count is equal to or greater than a first threshold; and
terminating, based on the determination that the iteration count is
equal to or greater than the first threshold, the iteration
process.
15. The method of claim 13, wherein at least one of the plurality
of iterations further includes: displaying, to a user, a
frequency-domain waveform of an RF pulse generated by the RFPA
based on the modified time-domain waveform updated in the at least
one of the plurality of iterations; receiving, from the user, an
instruction related to the updated time-domain waveform determined
in the at least one of the plurality of iterations; and
terminating, based on the received instruction, the iteration
process.
16. The method of claim 15, wherein the received instruction
includes that the updated RF pulse generated by the RFPA based on
the updated time-domain waveform generated in the at least one of
the plurality of iterations is acceptable.
Description
TECHNICAL FIELD
The present disclosure generally relates to magnetic resonance
imaging (MRI), and more specifically relates to systems and methods
for modifying radiofrequency (RF) pulses used in an MRI scan.
BACKGROUND
Magnetic resonance imaging (MRI) is widely used for medical
diagnosis. During an MRI scan, there may be one or more excitations
in each of which one or more slices of an object may be excited. In
an excitation, an excitation RF pulse may be applied to excite one
or more slices of the object in conjunction with a slice selective
gradient. Generally, a waveform generator of an MRI scanner may
generate an RF pulse. The RF pulse generated by the waveform
generator may be amplified using a radiofrequency power amplifier
(RFPA). The RFPA may amplify the RF pulse (e.g., the power of the
RF pulse, the voltage of the RF pulse) such that the amplified RF
pulse may drive the RF coils to generate a magnetic field of a
sufficient magnitude. However, the waveform of the amplified RF
pulse generated by the RFPA may be different from designed, which
is referred to as distortion. When the amplified RF pulse with
distortion is applied on the RF coils to generate a magnetic field,
the magnetic field together with a slice selective gradient may
excite one or more undesired slices, which may cause artifacts in
an image generated based on the MRI scan. Therefore, it is
desirable to provide systems and methods to reduce or eliminate the
effect of the distortion.
SUMMARY
In a first aspect of the present disclosure, a system for modifying
RF pulse infidelity may one or more storage devices and one or more
processors configured to communicate with the one or more storage
devices. The one or more storage devices may include a set of
instructions. When the one or more processors executing the set of
instructions, the one or more processors may be directed to perform
one or more of the following operations. The one or more processors
may obtain a designed time-domain waveform. The one or more
processors may direct a radio frequency power amplifier (RFPA) of a
magnetic resonance imaging (MRI) scanner to generate an output RF
pulse based on the designed time-domain waveform. The one or more
processors may measure an output time-domain waveform of the output
RF pulse. The one or more processors may determine, based on the
designed time-domain waveform and the output time-domain waveform,
a modified time-domain waveform corresponding to an excitation RF
pulse. The one or more processors may direct the MRI scanner to
generate, using a waveform generator and the RFPA and based on the
modified time-domain waveform, the excitation RF pulse to excite
one or more slices of an object in an MRI scan.
In some embodiments, the modified time-domain waveform is closer to
satisfying an execution capability criterion than the designed
time-domain waveform. The execution capability criterion may embody
a criterion for a refocusing flip angle of the designed RF
pulse.
In some embodiments, to determine the modified time-domain waveform
corresponding to the excitation RF pulse based on the designed
time-domain waveform and the output time-domain waveform, the one
or more processors may transform the designed time-domain waveform
into a designed frequency-domain waveform with one or more
excitation bands. The one or more processors may transform the
output time-domain waveform into an output frequency-domain
waveform. The one or more processors may determine one or more
frequency-domain sidebands in the output frequency-domain waveform
by comparing the designed frequency-domain waveform with the output
frequency-domain waveform. The one or more processors may determine
the modified time-domain waveform based on the one or more
frequency-domain sidebands.
In some embodiments, to determine the modified time-domain waveform
based on the one or more frequency-domain sidebands, the one or
more processors may select a portion of the output frequency-domain
waveform, the portion of the output frequency-domain waveform
including the one or more frequency-domain sidebands but not the
one or more excitation bands. The one or more processors may
determine a compensation frequency-domain waveform based on the
selected portion of the output frequency-domain waveform. The one
or more processors may transform the compensation frequency-domain
waveform into a compensation time-domain waveform. The one or more
processors may determine the modified time-domain waveform based on
the compensation time-domain waveform and the designed time-domain
waveform.
In some embodiments, a phase difference between the selected
portion of the output frequency-domain waveform and the
compensation frequency-domain waveform may be 180.degree..
In some embodiments, to determine the modified time-domain waveform
corresponding to the excitation RF pulse, the one or more
processors may repeatedly determine an updated time-domain waveform
in an iteration process including a plurality of successive
iterations until a termination criterion is satisfied. The updated
time-domain waveform determined at the end of the iteration process
may be the modified time-domain waveform.
In some embodiments, at least one of the plurality of iterations
may include determining the updated time-domain waveform based on
the designed time-domain waveform and a previous output time-domain
waveform. The previous output time-domain waveform may correspond
to the designed time-domain waveform in a first iteration of the
interation process or a previously updated time-domain waveform
determined in a previous iteration. The updated time-domain
waveform may correspond to an updated RF pulse. The at least one of
the plurality of iterations may also include directing the RFPA of
the MRI scanner to generate the updated RF pulse. The at least one
of the plurality of iterations may also include measuring an output
time-domain waveform of the updated RF pulse.
In some embodiments, at least one of the plurality of iterations
may further include determining an iteration count of iterations
that have been performed. The at least one of the plurality of
iterations may further include determining that the iteration count
is equal to or greater than a first threshold. The at least one of
the plurality of iterations may further include terminating, based
on the determination that the iteration count is equal to or
greater than the first threshold, the iteration process.
In some embodiments, at least one of the plurality of iterations
may further include displaying, to a user, a frequency-domain
waveform of an RF pulse generated by the RFPA based on the modified
time-domain waveform updated in the at least one of the plurality
of iterations. The at least one of the plurality of iterations may
further include receiving, from the user, an instruction related to
the updated time-domain waveform determined in the at least one of
the plurality of iterations. The at least one of the plurality of
iterations may further include terminating, based on the received
instruction, the iteration process.
In some embodiments, the received instruction includes that the
updated RF pulse generated by the RFPA based on the updated
time-domain waveform generated in the at least one of the plurality
of iterations is acceptable.
In some embodiments, the excitation RF pulse may be applied to
simultaneous multi-slice (SMS) imaging.
According to another aspect of the present disclosure, a method for
modifying RF pulse infidelity may include one or more of the
following operations. One or more processors may obtain a designed
time-domain waveform. The one or more processors may direct a radio
frequency power amplifier (RFPA) of a magnetic resonance imaging
(MRI) scanner to generate an output RF pulse based on the designed
time-domain waveform. The one or more processors may measure an
output time-domain waveform of the output RF pulse. The one or more
processors may determine, based on the designed time-domain
waveform and the output time-domain waveform, a modified
time-domain waveform corresponding to an excitation RF pulse. The
one or more processors may direct the MRI scanner to generate,
using a waveform generator and the RFPA and based on the modified
time-domain waveform, the excitation RF pulse to excite one or more
slices of an object in an MRI scan.
According to yet another aspect of the present disclosure, a
non-transitory computer readable medium may comprise at least one
set of instructions. The at least one set of instructions may be
executed by one or more processors of a computing device. The one
or more processors may obtain a designed time-domain waveform. The
one or more processors may direct a radio frequency power amplifier
(RFPA) of a magnetic resonance imaging (MRI) scanner to generate an
output RF pulse based on the designed time-domain waveform. The one
or more processors may measure an output time-domain waveform of
the output RF pulse. The one or more processors may determine,
based on the designed time-domain waveform and the output
time-domain waveform, a modified time-domain waveform corresponding
to an excitation RF pulse. The one or more processors may direct
the MRI scanner to generate, using a waveform generator and the
RFPA and based on the modified time-domain waveform, the excitation
RF pulse to excite one or more slices of an object in an MRI
scan.
According to yet another aspect of the present disclosure, a system
for modifying RF pulse infidelity may comprise: a waveform design
module configured to obtain a designed time-domain waveform; a
control module configured to direct a radio frequency power
amplifier (RFPA) of a magnetic resonance imaging (MRI) scanner to
generate an output RF pulse based on the designed time-domain
waveform; an output pulse acquisition module configured to measure
an output time-domain waveform of the output RF pulse; a waveform
modification module configured to determine, based on the designed
time-domain waveform and the output time-domain waveform, a
modified time-domain waveform corresponding to an excitation RF
pulse; and the control module configured to direct the MRI scanner
to generate, using a waveform generator and the RFPA and based on
the modified time-domain waveform, the excitation RF pulse to
excite one or more slices of an object in an MRI scan.
Additional features will be set forth in part in the description
which follows, and in part will become apparent to those skilled in
the art upon examination of the following and the accompanying
drawings or may be learned by production or operation of the
examples. The features of the present disclosure may be realized
and attained by practice or use of various aspects of the
methodologies, instrumentalities, and combinations set forth in the
detailed examples discussed below.
BRIEF DESCRIPTION OF THE DRAWINGS
The present disclosure is further described in terms of exemplary
embodiments. These exemplary embodiments are described in detail
with reference to the drawings. The drawings are not to scale.
These embodiments are non-limiting exemplary embodiments, in which
like reference numerals represent similar structures throughout the
several views of the drawings, and wherein:
FIG. 1 is a schematic diagram illustrating an exemplary MRI system
according to some embodiments of the present disclosure;
FIG. 2 is a schematic diagram illustrating an exemplary MRI scanner
according to some embodiments of the present disclosure;
FIG. 3 is a schematic diagram illustrating exemplary hardware
and/or software components of a computing device on which a
processing device may be implemented according to some embodiments
of the present disclosure;
FIG. 4 is a schematic diagram illustrating exemplary hardware
and/or software components of a mobile device on which a terminal
may be implemented according to some embodiments of the present
disclosure;
FIG. 5 is a block diagram illustrating an exemplary processing
device according to some embodiments of the present disclosure;
FIG. 6 is a flowchart illustrating an exemplary process for
modifying a time-domain waveform according to some embodiments of
the present disclosure;
FIG. 7 is a flowchart illustrating an exemplary process for
determining a modified time-domain waveform according to some
embodiments of the present disclosure;
FIG. 8 is a flowchart illustrating an exemplary process for
determining a modified time-domain waveform according to some
embodiments of the present disclosure;
FIG. 9 shows an exemplary designed time-domain waveform and an
exemplary corresponding output time-domain waveform according to
some embodiments of the present disclosure;
FIG. 10 shows an exemplary designed frequency-domain waveform
according to some embodiments of the present disclosure;
FIG. 11 shows an exemplary output frequency-domain waveform
according to some embodiments of the present disclosure;
FIG. 12 shows an exemplary corrected output frequency-domain
waveform according to some embodiments of the present
disclosure;
FIG. 13 is a schematic diagram illustrating an exemplary
simultaneous multi-slice (SMS) imaging according to some
embodiments of the present disclosure; and
FIG. 14 is a schematic diagram illustrating exemplary image
reconstruction in SMS imaging according to some embodiments of the
present disclosure.
DETAILED DESCRIPTION
In the following detailed description, numerous specific details
are set forth by way of examples in order to provide a thorough
understanding of the relevant disclosure. However, it should be
apparent to those skilled in the art that the present disclosure
may be practiced without such details. In other instances, well
known methods, procedures, systems, components, and/or circuitry
have been described at a relatively high-level, without detail, in
order to avoid unnecessarily obscuring aspects of the present
disclosure. Various modifications to the disclosed embodiments will
be readily apparent to those skilled in the art, and the general
principles defined herein may be applied to other embodiments and
applications without departing from the spirit and scope of the
present disclosure. Thus, the present disclosure is not limited to
the embodiments shown, but to be accorded the widest scope
consistent with the claims.
The terminology used herein is for the purpose of describing
particular example embodiments only and is not intended to be
limiting. As used herein, the singular forms "a," "an," and "the"
may be intended to include the plural forms as well, unless the
context clearly indicates otherwise. It will be further understood
that the terms "comprise," "comprises," and/or "comprising,"
"include," "includes," and/or "including," when used in this
specification, specify the presence of stated features, integers,
steps, operations, elements, and/or components, but do not preclude
the presence or addition of one or more other features, integers,
steps, operations, elements, components, and/or groups thereof.
It will be understood that the term "system," "unit," "module,"
and/or "block" used herein are one method to distinguish different
components, elements, parts, section or assembly of different level
in ascending order. However, the terms may be displaced by another
expression if they achieve the same purpose.
Generally, the word "module," "unit," or "block," as used herein,
refers to logic embodied in hardware or firmware, or to a
collection of software instructions. A module, a unit, or a block
described herein may be implemented as software and/or hardware and
may be stored in any type of non-transitory computer-readable
medium or other storage device. In some embodiments, a software
module/unit/block may be compiled and linked into an executable
program. It will be appreciated that software modules can be
callable from other modules/units/blocks or from themselves, and/or
may be invoked in response to detected events or interrupts.
Software modules/units/blocks configured for execution on computing
devices (e.g., processor 310 as illustrated in FIG. 3) may be
provided on a computer readable medium, such as a compact disc, a
digital video disc, a flash drive, a magnetic disc, or any other
tangible medium, or as a digital download (and can be originally
stored in a compressed or installable format that needs
installation, decompression, or decryption prior to execution).
Such software code may be stored, partially or fully, on a storage
device of the executing computing device, for execution by the
computing device. Software instructions may be embedded in
firmware, such as an EPROM. It will be further appreciated that
hardware modules/units/blocks may be included of connected logic
components, such as gates and flip-flops, and/or can be included of
programmable units, such as programmable gate arrays or processors.
The modules/units/blocks or computing device functionality
described herein may be implemented as software
modules/units/blocks, but may be represented in hardware or
firmware. In general, the modules/units/blocks described herein
refer to logical modules/units/blocks that may be combined with
other modules/units/blocks or divided into
sub-modules/sub-units/sub-blocks despite their physical
organization or storage.
It will be understood that when a unit, engine, module or block is
referred to as being "on," "connected to," or "coupled to," another
unit, engine, module, or block, it may be directly on, connected or
coupled to, or communicate with the other unit, engine, module, or
block, or an intervening unit, engine, module, or block may be
present, unless the context clearly indicates otherwise. As used
herein, the term "and/or" includes any and all combinations of one
or more of the associated listed items.
These and other features, and characteristics of the present
disclosure, as well as the methods of operation and functions of
the related elements of structure and the combination of parts and
economies of manufacture, may become more apparent upon
consideration of the following description with reference to the
accompanying drawings, all of which form a part of this disclosure.
It is to be expressly understood, however, that the drawings are
for the purpose of illustration and description only and are not
intended to limit the scope of the present disclosure. It is
understood that the drawings are not to scale.
An aspect of the present disclosure relates to systems and methods
for modifying a time-domain waveform relating to an excitation RF
pulse to compensate undesired sidebands in an amplified RF pulse
generated by RFPA. During an MRI scan, an MRI scanner may generate
an RF pulse from the modified time-domain waveform to excite the
one or more slices of the object in conjunction with a slice
selective gradient.
The following description is provided with reference to systems and
methods for modifying an excitation RF pulse. This is not intended
to limit the scope the present disclosure. For persons having
ordinary skills in the art, a certain amount of variations,
changes, and/or modifications may be deducted under the guidance of
the present disclosure. Those variations, changes, and/or
modifications do not depart from the scope of the present
disclosure.
During an MRI scan, there may be one or more excitations in each of
which one or more slices of an object may be excited. In an
excitation, an excitation RF pulse may be applied to excite one or
more slices of the object in conjunction with a slice selective
gradient. The excitation RF pulse and the slice selective gradient
may collaboratively determine which slice(s) of the object is/are
excited. In some embodiments, the systems and/or methods described
in this disclosure may be applied to single slice MR imaging and/or
multi-slice MR imaging (e.g., simultaneous multi-slice (SMS)
imaging). In the single slice MR imaging, one slice may be excited
at a time during the MRI scan. In the multi-slice MR imaging, more
than one slice may be excited at a time during the MRI scan. In SMS
imaging, more than one slice may be excited simultaneously in one
excitation.
FIG. 1 is a schematic diagram illustrating an exemplary MRI system
100 according to some embodiments of the present disclosure. As
illustrated, the MRI system 100 may include an MRI scanner 110, a
network 120, a terminal 130, a processing device 140, and a storage
device 150. The components of the MRI system 100 may be connected
in one or more of various ways. Mere by way of example, as
illustrated in FIG. 1, the MRI scanner 110 may be connected to the
processing device 140 through the network 120. As another example,
the MRI scanner 110 may be connected to the processing device 140
directly (as indicated by the bi-directional arrow in dotted lines
linking the MRI scanner 110 and the processing device 140). As a
further example, the storage device 150 may be connected to the
processing device 140 directly or through the network 120. As still
a further example, a terminal device (e.g., 130-1, 130-2, 130-3,
etc.) may be connected to the processing device 140 directly (as
indicated by the bi-directional arrow in dotted lines linking the
terminal 130 and the processing device 140) or through the network
120.
The MRI scanner 110 may scan an object located within its detection
region and generate a plurality of data relating to the object. In
the present disclosure, "subject" and "object" are used
interchangeably. Mere by way of example, the object may include a
patient, a man-made object, etc. As another example, the object may
include a specific portion, organ, and/or tissue of the patient.
For example, the object may include head, brain, neck, body,
shoulder, arm, thorax, cardiac, stomach, blood vessel, soft tissue,
knee, feet, or the like, or any combination thereof. In some
embodiments, the MRI scanner 110 may be a close-bore scanner or an
open-bore scanner. More description of the MRI scanner 110 may be
found elsewhere in the present disclosure. See, e.g., FIG. 2 and
the description thereof.
The network 120 may include any suitable network that can
facilitate the exchange of information and/or data for the MRI
system 100. In some embodiments, one or more components of the MRI
system 100 (e.g., the MRI scanner 110, the terminal 130, the
processing device 140, or the storage device 150) may communicate
information and/or data with one or more other components of the
MRI system 100 via the network 120. For example, the processing
device 140 may obtain signals of an RF pulse from the MRI scanner
110 via the network 120. In some embodiments, the network 120 may
be any type of wired or wireless network, or a combination thereof.
The network 120 may be and/or include a public network (e.g., the
Internet), a private network (e.g., a local area network (LAN), a
wide area network (WAN)), etc.), a wired network (e.g., an Ethernet
network), a wireless network (e.g., an 802.11 network, a Wi-Fi
network, etc.), a cellular network (e.g., a Long Term Evolution
(LTE) network), a frame relay network, a virtual private network
("VPN"), a satellite network, a telephone network, routers, hubs,
switches, server computers, and/or any combination thereof. Merely
by way of example, the network 120 may include a cable network, a
wireline network, a fiber-optic network, a telecommunications
network, an intranet, a wireless local area network (WLAN), a
metropolitan area network (MAN), a public telephone switched
network (PSTN), a Bluetooth.TM. network, a ZigBee.TM. network, a
near field communication (NFC) network, or the like, or any
combination thereof. In some embodiments, the network 120 may
include one or more network access points. For example, the network
120 may include wired and/or wireless network access points such as
base stations and/or internet exchange points through which one or
more components of the MRI system 100 may be connected to the
network 120 to exchange data and/or information.
The terminal 130 include a mobile device 130-1, a tablet computer
130-2, a laptop computer 130-3, or the like, or any combination
thereof. In some embodiments, the mobile device 130-1 may include a
smart home device, a wearable device, a smart mobile device, a
virtual reality device, an augmented reality device, or the like,
or any combination thereof. In some embodiments, the smart home
device may include a smart lighting device, a control device of an
intelligent electrical apparatus, a smart monitoring device, a
smart television, a smart video camera, an interphone, or the like,
or any combination thereof. In some embodiments, the wearable
device may include a smart bracelet, smart footgear, a pair of
smart glasses, a smart helmet, a smart watch, smart clothing, a
smart backpack, a smart accessory, or the like, or any combination
thereof. In some embodiments, the smart mobile device may include a
smartphone, a personal digital assistant (PDA), a gaming device, a
navigation device, a point of sale (POS) device, or the like, or
any combination thereof. In some embodiments, the virtual reality
device and/or the augmented reality device may include a virtual
reality helmet, a virtual reality glass, a virtual reality patch,
an augmented reality helmet, an augmented reality glass, an
augmented reality patch, or the like, or any combination thereof.
For example, the virtual reality device and/or the augmented
reality device may include a Google.TM. Glass, an Oculus Rift, a
Hololens, a Gear VR, etc. In some embodiments, the terminal 130 may
remotely operate the MRI scanner 110. In some embodiments, the
terminal 130 may operate the MRI scanner 110 via a wireless
connection. In some embodiments, the terminal 130 may receive
information and/or instructions inputted by a user, and send the
received information and/or instructions to the MRI scanner 110 or
to the processing device 140 via the network 120. In some
embodiments, the terminal 130 may receive data and/or information
from the processing device 140. In some embodiments, the terminal
130 may be part of the processing device 140. In some embodiments,
the terminal 130 may be omitted.
The processing device 140 may process data and/or information
obtained from the MRI scanner 110, the terminal 130, and/or the
storage device 150. For example, the processing device 140 may
obtain a designed time-domain waveform from the storage device 150
and correct the designed time-domain waveform. In some embodiments,
the processing device 140 may be a single server, or a server
group. The server group may be centralized, or distributed. In some
embodiments, the processing device 140 may be local or remote. For
example, the processing device 140 may access information and/or
data stored in the MRI scanner 110, the terminal 130, and/or the
storage device 150 via the network 120. As another example, the
processing device 140 may be directly connected to the MRI scanner
110, the terminal 130, and/or the storage device 150 to access
stored information and/or data. In some embodiments, the processing
device 140 may be implemented on a cloud platform. Merely by way of
example, the cloud platform may include a private cloud, a public
cloud, a hybrid cloud, a community cloud, a distributed cloud, an
inter-cloud, a multi-cloud, or the like, or any combination
thereof. In some embodiments, the processing device 140 may be
implemented on a computing device 300 having one or more components
illustrated in FIG. 3 in the present disclosure.
The storage device 150 may store data and/or instructions. In some
embodiments, the storage device 150 may store data obtained from
the terminal 130 and/or the processing device 140. For example, the
storage device 150 may store a designed time-domain waveform
designed by a user (e.g., a doctor, an imaging engineer). In some
embodiments, the storage device 150 may store data and/or
instructions that the processing device 140 may execute or use to
perform exemplary methods described in the present disclosure. For
example, the storage device 150 may store instructions that the
processing device 140 may execute or use to determine a modified
time-domain waveform. In some embodiments, the storage device 150
may include a mass storage device, a removable storage device, a
volatile read-and-write memory, a read-only memory (ROM), or the
like, or any combination thereof. Exemplary mass storage may
include a magnetic disk, an optical disk, a solid-state drive, etc.
Exemplary removable storage may include a flash drive, a floppy
disk, an optical disk, a memory card, a zip disk, a magnetic tape,
etc. Exemplary volatile read-and-write memory may include a random
access memory (RAM). Exemplary RAM may include a dynamic RAM
(DRAM), a double date rate synchronous dynamic RAM (DDR SDRAM), a
static RAM (SRAM), a thyristor RAM (T-RAM), and a zero-capacitor
RAM (Z-RAM), etc. Exemplary ROM may include a mask ROM (MROM), a
programmable ROM (PROM), an erasable programmable ROM (PEROM), an
electrically erasable programmable ROM (EEPROM), a compact disk ROM
(CD-ROM), and a digital versatile disk ROM, etc. In some
embodiments, the storage device 150 may be implemented on a cloud
platform. Merely by way of example, the cloud platform may include
a private cloud, a public cloud, a hybrid cloud, a community cloud,
a distributed cloud, an inter-cloud, a multi-cloud, or the like, or
any combination thereof.
In some embodiments, the storage device 150 may be connected to the
network 120 to communicate with one or more components of the MRI
system 100 (e.g., the processing device 140, the terminal 130,
etc.). One or more components of the MRI system 100 may access the
data or instructions stored in the storage device 150 via the
network 120. In some embodiments, the storage device 150 may be
directly connected to or communicate with one or more components of
the MRI system 100 (e.g., the processing device 140, the terminal
130, etc.). In some embodiments, the storage device 150 may be part
of the processing device 140.
FIG. 2 is a schematic diagram illustrating an exemplary MRI scanner
according to some embodiments of the present disclosure. As
illustrated, the main magnet 201 may generate a first magnetic
field (or referred to as a main magnetic field) that may be applied
to an object (also referred to as a subject) exposed inside the
field. The main magnet 201 may also control the homogeneity of the
generated main magnetic field. Some shim coils may be in the main
magnet 201. The shim coils placed in the gap of the main magnet 201
may compensate for the inhomogeneity of the magnetic field of the
main magnet 201. Gradient coils 202 may be located inside the main
magnet 201. The gradient coils 202 may generate a second magnetic
field (or referred to as a gradient field). The gradient coils 202
may distort the main field generated by the main magnet 201 so that
the magnetic orientations of the protons of an object may vary as a
function of their positions inside the gradient field. The gradient
coils 202 may include X coils, Y coils, and/or Z coils (not shown
in FIG. 2). In some embodiments, the Z coils may be designed based
on circular (Maxwell) coils, while the X coils and the Y coils may
be designed on the basis of the saddle (Golay) coil configuration.
The three sets of coils may generate three different magnetic
fields that are used for position encoding. The gradient coils 202
may allow spatial encoding of MR signals for image construction.
The gradient coils 202 may be connected with one or more of an X
gradient amplifier 204, a Y gradient amplifier 205, or a Z gradient
amplifier 206. One or more of the three amplifiers may be connected
to a waveform generator 216. The waveform generator 216 may
generate gradient waveforms that are applied to the X gradient
amplifier 204, the Y gradient amplifier 205, and/or the Z gradient
amplifier 206. An amplifier may amplify a waveform. An amplified
waveform may be applied to one of the coils in the gradient coils
202 to generate a magnetic field in the X-axis, the Y-axis, or the
Z-axis, respectively. The gradient coils 202 may be designed for
either a close-bore MRI scanner or an open-bore MRI scanner. In
some instances, all three sets of coils of the gradient coils 202
may be energized and three gradient fields may be generated
thereby. In some embodiments of the present disclosure, the X coils
and Y coils may be energized to generate the gradient fields in the
X direction and the Y direction.
In some embodiments, RF coils 203 may be in connection with RF
electronics 209 that may be configured or used as one or more
integrated circuits (ICs) functioning as a waveform transmitter
and/or a waveform receiver. The RF electronics 209 may be connected
to a radiofrequency power amplifier (RFPA) 207 and an
analog-to-digital converter (ADC) 208.
The RF coils 203 may serve as transmitters, receivers, or both.
When used as transmitters, the RF coils 203 may generate a third
magnetic field that is utilized to generate MR signals for image
generation. The third magnetic field may be perpendicular to the
main magnetic field. The waveform generator 216 may generate an RF
pulse. The RF pulse may be amplified by the RFPA 207, processed by
the RF electronics 209, and applied to the RF coils 203 to generate
a third magnetic field in response to a powerful current generated
by the RF electronics 209 based on the amplified RF pulse. When
used as receivers, the RF coils may be responsible for detecting MR
signals (e.g., echoes).
In some embodiments, the RFPA 207 may amplify an RF pulse (e.g.,
the power of the RF pulse, the voltage of the RF pulse) such that
an amplified RF pulse is generated to drive the RF-coils 203. The
RFPA 207 may include a transistor-based RFPA, a vacuum tube-based
RFPA, or the like, or any combination thereof. The transistor-based
RFPA may include one or more transistors. The vacuum tube-based
RFPA may include a triode, a tetrode, a klystron, or the like, or
any combination thereof. In some embodiments, the RFPA 207 may
include a linear RFPA, or a nonlinear RFPA. In some embodiments,
the RFPA 207 may include one or more RFPAs.
FIG. 3 is a schematic diagram illustrating exemplary hardware
and/or software components of a computing device on which the
processing device 140 may be implemented according to some
embodiments of the present disclosure. As illustrated in FIG. 3,
the computing device 300 may include a processor 310, a storage
320, an input/output (I/O) 330, and a communication port 340.
The processor 310 may execute computer instructions (program code)
and perform functions of the processing device 140 in accordance
with techniques described herein. The computer instructions may
include routines, programs, objects, components, signals, data
structures, procedures, modules, and functions, which perform
particular functions described herein. For example, the processor
310 may obtain a designed time-domain waveform from the storage
device 150 and correct the designed time-domain waveform. In some
embodiments, the processor 310 may include a microcontroller, a
microprocessor, a reduced instruction set computer (RISC), an
application specific integrated circuits (ASICs), an
application-specific instruction-set processor (ASIP), a central
processing unit (CPU), a graphics processing unit (GPU), a physics
processing unit (PPU), a microcontroller unit, a digital signal
processor (DSP), a field programmable gate array (FPGA), an
advanced RISC machine (ARM), a programmable logic device (PLD), any
circuit or processor capable of executing one or more functions, or
the like, or any combinations thereof.
Merely for illustration purposes, only one processor is described
in the computing device 300. However, it should be note that the
computing device 300 in the present disclosure may also include
multiple processors, thus operations and/or method steps that are
performed by one processor as described in the present disclosure
may also be jointly or separately performed by the multiple
processors. For example, if in the present disclosure the processor
of the computing device 300 executes both step A and step B, it
should be understood that step A and step B may also be performed
by two different processors jointly or separately in the computing
device 300 (e.g., a first processor executes step A and a second
processor executes step B, or the first and second processors
jointly execute steps A and B).
The storage 320 may store data/information obtained from the MRI
scanner 110, the terminal 130, the storage device 150, or any other
component of the MRI system 100. In some embodiments, the storage
320 may include a mass storage device, a removable storage device,
a volatile read-and-write memory, a read-only memory (ROM), or the
like, or any combination thereof. For example, the mass storage
device may include a magnetic disk, an optical disk, a solid-state
drive, etc. The removable storage device may include a flash drive,
a floppy disk, an optical disk, a memory card, a zip disk, a
magnetic tape, etc. The volatile read-and-write memory may include
a random access memory (RAM). The RAM may include a dynamic RAM
(DRAM), a double date rate synchronous dynamic RAM (DDR SDRAM), a
static RAM (SRAM), a thyristor RAM (T-RAM), and a zero-capacitor
RAM (Z-RAM), etc. The ROM may include a mask ROM (MROM), a
programmable ROM (PROM), an erasable programmable ROM (PEROM), an
electrically erasable programmable ROM (EEPROM), a compact disk ROM
(CD-ROM), and a digital versatile disk ROM, etc. In some
embodiments, the storage 320 may store one or more programs and/or
instructions to perform exemplary methods described in the present
disclosure. For example, the storage 320 may store a program for
the processing device 140 for determining a modified time-domain
waveform corresponding to an excitation RF pulse to excite one or
more slices of an object in conjunction with a slice selective
gradient in an excitation in an MRI scan.
The I/O 330 may input or output signals, data, or information. In
some embodiments, the I/O 330 may enable a user interaction with
the processing device 140. For example, the processing device may
display an image through the I/O 330. In some embodiments, the I/O
330 may include an input device and an output device. Exemplary
input devices may include a keyboard, a mouse, a touch screen, a
microphone, or the like, or a combination thereof. Exemplary output
devices may include a display device, a loudspeaker, a printer, a
projector, or the like, or a combination thereof. Exemplary display
devices may include a liquid crystal display (LCD), a
light-emitting diode (LED)-based display, a flat panel display, a
curved screen, a television device, a cathode ray tube (CRT), or
the like, or a combination thereof.
The communication port 340 may be connected to a network (e.g., the
network 120) to facilitate data communications. The communication
port 340 may establish connections between the processing device
140 and the MRI scanner 110, the terminal 130, or the storage
device 150. The connection may be a wired connection, a wireless
connection, or combination of both that enables data transmission
and reception. The wired connection may include an electrical
cable, an optical cable, a telephone wire, or the like, or any
combination thereof. The wireless connection may include Bluetooth,
Wi-Fi, WiMax, WLAN, ZigBee, mobile network (e.g., 3G, 4G, 5G,
etc.), or the like, or a combination thereof. In some embodiments,
the communication port 340 may be a standardized communication
port, such as RS232, RS485, etc. In some embodiments, the
communication port 340 may be a specially designed communication
port. For example, the communication port 340 may be designed in
accordance with the digital imaging and communications in medicine
(DICOM) protocol.
FIG. 4 is a schematic diagram illustrating exemplary hardware
and/or software components of a mobile device on which the terminal
130 may be implemented according to some embodiments of the present
disclosure. As illustrated in FIG. 4, the mobile device 400 may
include a communication platform 410, a display 420, a graphic
processing unit (GPU) 430, a central processing unit (CPU) 440, an
I/O 450, a memory 460, and a storage 490. In some embodiments, any
other suitable component, including but not limited to a system bus
or a controller (not shown), may also be included in the mobile
device 400. In some embodiments, a mobile operating system 470
(e.g., iOS, Android, Windows Phone, etc.) and one or more
applications 480 may be loaded into the memory 460 from the storage
490 in order to be executed by the CPU 440. The applications 480
may include a browser or any other suitable mobile apps for
receiving and rendering information relating to image processing or
other information from the processing device 140. User interactions
with the information stream may be achieved via the I/O 450 and
provided to the processing device 140 and/or other components of
the MRI system 100 via the network 120.
To implement various modules, units, and their functionalities
described in the present disclosure, computer hardware platforms
may be used as the hardware platform(s) for one or more of the
elements described herein. The hardware elements, operating systems
and programming languages of such computers are conventional in
nature, and it is presumed that those skilled in the art are
adequately familiar therewith to adapt those technologies to the
blood pressure monitoring as described herein. A computer with user
interface elements may be used to implement a personal computer
(PC) or another type of work station or terminal device, although a
computer may also act as a server if appropriately programmed. It
is believed that those skilled in the art are familiar with the
structure, programming and general operation of such computer
equipment and as a result the drawings should be
self-explanatory.
FIG. 5 is a block diagram illustrating an exemplary processing
device according to some embodiments of the present disclosure. The
processing device 140 may be implemented on the computing device
300 (e.g., the processor 310) illustrated in FIG. 3. During an MRI
scan, there may be one or more excitations in each of which one or
more slices of an object may be excited. In an excitation, an
excitation RF pulse may be applied to excite one or more slices of
the object in conjunction with a slice selective gradient. The
excitation RF pulse and the slice selective gradient may
collaboratively determine which slice(s) of the object is/are
excited. The slice of the object refers to a cross-section of the
object. The cross-section may be parallel to a plane of any
direction, such as a transverse plane, a sagittal plane, or a
coronal plane of the object.
The processing device 140 may include a waveform design module 510,
a control module 520, an output pulse acquisition module 530, and a
waveform modification module 540.
The waveform design module 510 may be configured to obtain a
designed time-domain waveform. A time-domain waveform may be a
scanning sequence indicating a relationship between the time and
the magnitude/phase of an RF pulse. The designed time-domain
waveform may include a control sequence. The control sequence may
be normally defined as a measurement protocol, which has been
created in advance and can be retrieved (e.g., from a memory) for a
specific measurement. The retrieved protocol can, if necessary, be
modified on site by a user (e.g., a doctor, an imaging engineer),
who can provide additional control parameters such as, for example,
a defined slice interval of a stack of slices to be measured, a
slice thickness, etc. The control sequence (also designated as a
pulse sequence) is then calculated on the basis of all of these
control parameters. The pulse sequence may comprise a value of a
flip angle that can be influenced with a refocusing pulse. The
value of the flip angle may be within a value range between 90
degrees and 180 degrees. In some embodiments, a user (e.g., a
doctor, or an imaging engineer) of the MRI system 100 may input,
through an interface of the processing device 140, user
specifications including, e.g., one or more parameters regarding a
desired time-domain waveform. The waveform design module 510 may
obtain a designed time-domain waveform according to the user
specifications. The user specifications may include the number of
slices of an object to be scanned in an excitation of an MRI scan,
the locations of the slices of the object to be scanned in the
excitaton of the MRI scan, one or more parameters regarding the
excitation bands (e.g., peak 1010 and peak 1020 shown in FIG. 10)
used to excite the one or more slices, parameters regarding a slice
selective gradient, or the like, or any combination thereof.
Exemplary parameters regarding an excitation band may include a
frequency range (e.g., from -3 kHz to 3 kHz), the magnitude of
signals within the frequency range, or the like, or a combination
thereof. In some embodiments, each of the one or more excitation
bands may be used to excite a slice of the object in conjunction
with a slice selective gradient. One or more slices may be excited
based on the one or more excitation bands and a slice selective
gradient. For instance, multiple slices of the object may be
excited simultaneously based on multiple excitation bands and a
slice selective gradient. In some embodiments, the designed
time-domain waveform may be determined in advance and may be stored
in a storage medium (e.g., the storage device 150, the storage
320). The waveform design module 510 may access the storage medium
(e.g., the storage device 150, the storage 320) to obtain the
designed time-domain waveform.
The control module 520 may be configured to direct an RFPA (e.g.,
the RFPA 207 in FIG. 2) of an MRI scanner (e.g., the MRI scanner
110) to generate an output RF pulse based on a time-domain
waveform. In some embodiments, the control module 520 may direct
the waveform generator 216 to generate an input RF pulse based on a
time-domain waveform, and direct the waveform generator 216 to
transmit output signals of the generated input RF pulse to the RFPA
207. The control module 520 may direct the RFPA 207 to amplify the
input RF pulse (e.g., the power of the input RF pulse, the voltage
of the input RF pulse) and generate an output RF pulse.
For example, the control module 520 may direct the waveform
generator 216 and the RFPA 207 to generate an output RF pulse based
on a designed time-domain waveform. See, e.g., FIG. 6 and the
description thereof. As another example, the control module 520 may
direct the waveform generator 216 and the RFPA 207 to generate an
updated output RF pulse based on an updated time-domain waveform.
See, e.g., FIG. 8 and the description thereof. As still another
example, the control module 520 may direct the waveform generator
216 and the RFPA 207 to generate an excitation RF pulse based on a
modified time-domain waveform. The excitation RF pulse may be
applied to excite one or more slices of an object in conjunction
with a slice selective gradient.
The output pulse acquisition module 530 may be configured to
measure an output time-domain waveform of the output RF pulse
generated by the RFPA (e.g., the RFPA 207). The output RF pulse
generated by the RFPA 207 may be sent to the ADC 208. The ADC 208
may transform analog signals of the output RF pulse into digital
signals of the output RF pulse. The digital signals of the output
RF pulse may be sent to the output pulse acquisition module 530.
The output pulse acquisition module 530 may collect the signals of
the output RF pulse and measure the output time-domain waveform
based on the collected signals of the output RF pulse. For example,
the output pulse acquisition module 530 may measure an output
time-domain waveform of an output RF pulse generated by the RFPA
207 based on the designed time-domain waveform. See, e.g., FIG. 6
and the description thereof. As another example, the output pulse
acquisition module 530 may measure an output time-domain waveform
of an updated RF pulse generated by the RFPA 207 based on an
updated time-domain waveform. See, e.g., FIG. 8 and the description
thereof.
The waveform modification module 540 may be configured to determine
a modified time-domain waveform corresponding to an excitation RF
pulse based on the designed time-domain waveform and the output
time-domain waveform. In general, an output RF pulse generated by
the RFPA 207 based on the designed time-domain waveform may be
applied to the RF coils 203 to generate an RF magnetic field to
excite one or more slices of the object in conjunction with a slice
selective gradient in an excitation in the MRI scan. However, the
time-domain (or frequency-domain) waveform of the output RF pulse
generated by the RFPA 207 based on the designed time-domain
waveform may be different from the designed time-domain (or
frequency-domain) waveform, which may be referred to as distortion.
For example, as shown in FIG. 9, magnitude 910 of the output
time-domain waveform corresponding to a time point is larger than
and/or different from magnitude 920 of the designed time-domain
waveform corresponding to the same time point. The distortion may
lead to one or more sidebands (also referred to as frequency-domain
sidebands) in a frequency-domain waveform of the output RF pulse,
different from the frequency-domain waveform corresponding to the
designed time-domain waveform (e.g., a designed frequency-domain
waveform). A frequency-domain waveform may illustrate a
relationship between a frequency and the magnitude/phase of an RF
pulse. A sideband may correspond to excitation frequencies
different from any designed excitation bands. The sideband may
excite an undesired slice (e.g., a slice different from the one or
more slices intended to be excited in an excitation) of the object,
which may cause artifacts in an image generated based on the MRI
scan. For example, as shown in FIG. 10, in the frequency-domain
waveform corresponding to the designed time-domain waveform, there
are only two excitation bands (e.g., peak 1010 and peak 1020) that
are used to excite two slices of the object. As shown in FIG. 11,
in the frequency-domain waveform of the output RF pulse, besides
the two excitation bands (e.g., peak 1010 and peak 1020), there are
sidebands (e.g., peak 1102, peak 1104, peak 1106, peak 1108).
Therefore, the waveform modification module 540 may correct the
designed time-domain waveform to eliminate or reduce the
sideband(s) in the frequency-domain waveform of the output RF
pulse. Description regarding the modification of the designed
time-domain waveform may be found elsewhere in the present
disclosure. See, e.g., FIG. 7 and FIG. 8, and the description
thereof.
In some embodiments, the modified time-domain waveform may
correspond to a desired excitation profile. The desired excitation
profile may refer to a frequency-domain waveform of an output RF
pulse generated by the RFPA 207 based on an RF pulse with the
modified time-domain waveform. In some embodiments, compared to the
designed frequency-domain waveform, no visible sidebands or
sidebands whose magnitude exceeds a threshold is present in the
desired excitation profile.
During the excitation in the MRI scan, an excitation RF pulse may
be generated using the waveform generator 216 and the RFPA 207
based on the modified time-domain waveform, and the excitation RF
pulse may be applied to the RF coils 203 to generate an RF magnetic
field that is imposed to the object to excite the one or more
slices in conjunction with a slice selective gradient.
The modules in the processing device 140 may be connected to or
communicate with each other via a wired connection or a wireless
connection. The wired connection may include a metal cable, an
optical cable, a hybrid cable, or the like, or any combination
thereof. The wireless connection may include a Local Area Network
(LAN), a Wide Area Network (WAN), a Bluetooth, a ZigBee, a Near
Field Communication (NFC), or the like, or any combination thereof.
Two or more of the modules may be combined as a single module, and
any one of the modules may be divided to two or more units. For
example, the waveform design module 510 may be integrated into the
output pulse acquisition module 530 as a single module that may
both obtain a designed time-domain waveform, and determine an
output time-domain waveform. As another example, the waveform
design module 510 may be divided into two units. The first unit may
be configured to obtain user specifications input by a user. The
second unit may be configured to obtain a designed time-domain
waveform based on the user specifications.
It should be noted that the above description is merely provided
for the purposes of illustration, and not intended to limit the
scope of the present disclosure. For persons having ordinary skills
in the art, multiple variations and modifications may be made under
the teachings of the present disclosure. However, those variations
and modifications do not depart from the scope of the present
disclosure. For example, the processing device 140 may further
include a storage module (not shown in FIG. 5). The storage module
may be configured to store data generated during any process
performed by any component of in the processing device 140. As
another example, each of components of the processing device 140
may include a storage apparatus. Additionally or alternatively, the
components of the computing device 120 may share a common storage
apparatus.
FIG. 6 is a flowchart illustrating an exemplary process for
modifying a time-domain waveform according to some embodiments of
the present disclosure. The process 600 may be implemented in the
MRI system 100 illustrated in FIG. 1. For example, the process 600
may be stored in the storage device 150 and/or the storage 320 in
the form of instructions (e.g., an application), and invoked and/or
executed by the processing device 140 (e.g., the processor 310
illustrated in FIG. 3, or one or more modules in the processing
device 140 illustrated in FIG. 5). The operations of the
illustrated process presented below are intended to be
illustrative. In some embodiments, the process 600 may be
accomplished with one or more additional operations not described,
and/or without one or more of the operations discussed.
Additionally, the order in which the operations of the process 600
as illustrated in FIG. 6 and described below is not intended to be
limiting.
During an MRI scan, there may be one or more excitations in each of
which one or more slices of an object may be excited. In an
excitation, an excitation RF pulse may be applied to excite one or
more slices of the object in conjunction with a slice selective
gradient. The excitation RF pulse and the slice selective gradient
may collaboratively determine which slice(s) of the object is/are
excited. A slice of the object refers to a cross-section of the
object. The cross-section may be parallel to a plane of any
direction, such as a transverse plane, a sagittal plane, or a
coronal plane of the object.
In 610, the waveform design module 510 may obtain a designed
time-domain waveform. A time-domain waveform may be a scanning
sequence illustrating a relationship between the time and the
magnitude/phase of an RF pulse. In some embodiments, a user (e.g.,
a doctor, or an imaging engineer) of the MRI system 100 may input,
through an interface of the processing device 140, user
specifications. The waveform design module 510 may obtain the
designed time-domain waveform according to the user specifications.
The user specifications may include the number of slices of the
object to be scanned in an excitaton of an MRI scan, the locations
of the slices of the object to be scanned in the excitaton of the
MRI scan, parameters regarding one or more excitation bands (e.g.,
peak 1010 and peak 1020 shown in FIG. 10) used to excite the one or
more slices, parameters regarding a slice selective gradient, or
the like, or any combination thereof. Exemplary parameters of an
excitation band may include a frequency range (e.g., from -3 kHz to
3 kHz), the magnitude of signals within the frequency range, or the
like, or a combination thereof. In some embodiments, each of the
one or more excitation bands may be used to excite a slice of the
object in conjunction with a slice selective gradient. One or more
slices may be excited based on the one or more excitation bands and
a slice selective gradient. For instance, multiple slices of the
object may be excited simultaneously based on multiple excitation
bands and a slice selective gradient. In some embodiments, the
designed time-domain waveform may be determined in advance and may
be stored in a storage medium (e.g., the storage device 150, the
storage 320). The waveform design module 510 may retrieve the
designed time-domain waveform from the storage medium (e.g., the
storage device 150, the storage 320).
In 620, the control module 520 may direct an RFPA (e.g., the RFPA
207 in FIG. 2) of an MRI scanner (e.g., the MRI scanner 110) to
generate an output RF pulse based on a time-domain waveform (e.g.,
the initially designed waveform or the corrected waveform). In some
embodiments, the control module 520 may direct the waveform
generator 216 to generate an input RF pulse based on the designed
time-domain waveform, and direct the waveform generator 216 to
transmit output signals of the generated input RF pulse to the RFPA
207. The control module 520 may direct the RFPA 207 to amplify the
input RF pulse (e.g., the power of the input RF pulse, the voltage
of the input RF pulse) and generate an output RF pulse.
In 630, the output pulse acquisition module 530 may measure an
output time-domain waveform of the output RF pulse generated by the
RFPA (e.g., the RFPA 207) based on the time-domain waveform (e.g.,
the initially designed waveform or the corrected waveform). The
output RF pulse generated by the RFPA 207 may be sent to the ADC
208. The ADC 208 may transform analog signals of the output RF
pulse into digital signals of the output RF pulse. The digital
signals of the output RF pulse may be sent to the output pulse
acquisition module 530. The output pulse acquisition module 530 may
collect the signals of the output RF pulse and measure the output
time-domain waveform based on the collected signals of the output
RF pulse.
In 640, the waveform modification module 540 may determine a
modified time-domain waveform based on the designed time-domain
waveform and the output time-domain waveform. In general, an output
RF pulse generated by the RFPA 207 based on the designed
time-domain waveform may be applied to the RF coils 203 to generate
an RF magnetic field to excite one or more slices of the object in
conjunction with a slice selective gradient in an excitation in the
MRI scan. However, the time-domain (or frequency-domain) waveform
of the output RF pulse generated by the RFPA 207 based on the
designed time-domain waveform may be different from the designed
time-domain (or frequency-domain) waveform, which may be referred
to as distortion. For example, as shown in FIG. 9, magnitude 910 of
the output time-domain waveform corresponding to a time point is
larger than and/or different from magnitude 920 of the designed
time-domain waveform corresponding to the same time point. The
distortion may lead to one or more sidebands (also referred to as
frequency-domain sidebands) in a frequency-domain waveform of the
output RF pulse, different from the frequency-domain waveform
corresponding to the designed time-domain waveform (e.g., a
designed frequency-domain waveform). A sideband may correspond to
excitation frequencies different from any designed excitation
bands. The sideband may excite an undesired slice (e.g., a slice
different from the one or more slices intended to be excited in an
excitation) of the object, which may cause artifacts in an image
generated based on the MRI scan. For example, as shown in FIG. 10,
in the frequency-domain waveform corresponding to the designed
time-domain waveform (e.g., a designed frequency-domain waveform),
there are only two excitation bands (e.g., peak 1010 and peak 1020)
that are used to excite two slices of the object. As shown in FIG.
11, in the frequency-domain waveform of the output RF pulse,
besides the two excitation bands (e.g., peak 1010 and peak 1020),
there are sidebands (e.g., peak 1102, peak 1104, peak 1106, peak
1108). Therefore, the waveform modification module 540 may correct
the designed time-domain waveform to eliminate or reduce the
sideband(s) in the frequency-domain waveform of the output RF
pulse. Description regarding the modification of the designed
time-domain waveform may be found elsewhere in the present
disclosure. See, e.g., FIG. 7 and FIG. 8, and the description
thereof.
In some embodiments, the modified time-domain waveform may
correspond to a desired excitation profile. The desired excitation
profile may refer to a frequency-domain waveform of an output RF
pulse generated by the RFPA 207 based on the modified time-domain
waveform. In some embodiments, compared to the frequency-domain
waveform corresponding to the designed time-domain waveform (e.g.,
a designed frequency-domain waveform), no visible sidebands or
sidebands whose magnitude exceeds a threshold is present in the
desired excitation profile.
During the excitation in the MRI scan, an excitation RF pulse may
be generated using the waveform generator 216 and the RFPA 207
based on the modified time-domain waveform, and the excitation RF
pulse may be applied to the RF coils 203 to generate an RF magnetic
field to excite one or more slices of the object in conjunction
with a slice selective gradient.
It should be noted that the above description of the process for
determining the modified time-domain waveform is provided for the
purposes of illustration, and is not intended to limit the scope of
the present disclosure. For persons having ordinary skills in the
art, multiple variations and modifications may be made under the
teachings of the present disclosure. However, those variations and
modifications do not depart from the scope of the present
disclosure.
FIG. 7 is a flowchart illustrating an exemplary process for
determining a modified time-domain waveform according to some
embodiments of the present disclosure. The process 700 may be
implemented in the MRI system 100 illustrated in FIG. 1. For
example, the process 700 may be stored in the storage device 150
and/or the storage 320 in the form of instructions (e.g., an
application), and invoked and/or executed by the processing device
140 (e.g., the processor 310 illustrated in FIG. 3, or one or more
modules in the processing device 140 illustrated in FIG. 5). The
operations of the illustrated process presented below are intended
to be illustrative. In some embodiments, the process 700 may be
accomplished with one or more additional operations not described,
and/or without one or more of the operations discussed.
Additionally, the order in which the operations of the process 700
as illustrated in FIG. 7 and described below is not intended to be
limiting. In some embodiments, operation 640 illustrated in FIG. 6
may be performed according to the process 700.
In 720, the waveform modification module 540 may transform a
designed time-domain waveform into a designed frequency-domain
waveform with one or more excitation bands. In some embodiments,
the waveform modification module 540 may transform the designed
time-domain waveform into the designed frequency-domain waveform by
Fourier transform.
In 730, the waveform modification module 540 may transform an
output time-domain waveform into an output frequency-domain
waveform. In some embodiments, the waveform modification module 540
may transform the output time-domain waveform into the output
frequency-domain waveform by Fourier transform.
In 740, the waveform modification module 540 may determine one or
more sidebands (also referred to as frequency-domain sidebands) in
the output frequency-domain waveform by comparing the designed
frequency-domain waveform with the output frequency-domain
waveform. As used herein, a frequency-domain sideband may refer to
undesired excitation in the frequency-domain representation of the
RFPA output signal compared with the designed frequency-domain
waveform profile. In some embodiments, the designed
frequency-domain waveform may include one or more excitation bands
(e.g., peak 1010 and/or peak 1020 in FIG. 10) that are used to
excite one or more slices of the object in an excitation. The
output frequency-domain waveform may include the one or more
excitation bands (e.g., peak 1010 and/or peak 1020 in FIG. 11)
corresponding to the one or more excitation bands in the designed
frequency-domain waveform, and one or more sidebands (e.g., peak
1102, peak 1104, peak 1106, or peak 1108 in FIG. 11).
In 745, the waveform modification module 540 may select a portion
(e.g., 1130 and/or 1140 in FIG. 11) of the output frequency-domain
waveform. The selected portion of the output frequency-domain
waveform may include the one or more frequency-domain sidebands but
not the one or more excitation bands.
In 750, the waveform modification module 540 may determine a
compensation frequency-domain waveform based on the selected
portion of the output frequency-domain waveform. A phase difference
between the compensation frequency-domain waveform and the selected
portion of the output frequency-domain waveform may be 180.degree..
The waveform modification module 540 may determine the compensation
frequency-domain waveform by reversing the phase of the selected
portion of the output frequency-domain waveform.
As used herein, a compensation frequency-domain waveform may
partially or completely cancel out the one or more frequency-domain
sidebands present in the output frequency-domain waveform.
In 760, the waveform modification module 540 may transform the
compensation frequency-domain waveform into a compensation
time-domain waveform. In some embodiments, the waveform
modification module 540 may transform the compensation
frequency-domain waveform into the compensation time-domain
waveform by inverse Fourier transform.
In 770, the waveform modification module 540 may determine a
modified time-domain waveform based on the compensation time-domain
waveform and the designed time-domain waveform. In some
embodiments, the waveform modification module 540 may combine the
designed time-domain waveform with the compensation time-domain
waveform to generate the modified time-domain waveform.
In some embodiments, to compensate the one or more sidebands in the
output frequency-domain waveform, the waveform modification module
540 may determine one or more compensation frequency-domain
sidebands corresponding to the one or more sidebands in the output
frequency-domain waveform. A phase difference between a sideband in
the output frequency-domain waveform and the corresponding
compensation frequency-domain sideband may be 180.degree.. As used
herein, a compensation frequency-domain sideband may partially or
completely cancel out the corresponding sideband present in the
output frequency-domain waveform.
The waveform modification module 540 may transform the one or more
compensation frequency-domain sidebands to the time domain by
Fourier transform. The waveform modification module 540 may
determine the modified time-domain waveform based on the designed
time-domain waveform and the representation of the one or more
compensation frequency-domain sidebands in the time domain.
It should be noted that the above description is merely provided
for the purposes of illustration, and not intended to limit the
scope of the present disclosure. For persons having ordinary skills
in the art, multiple variations and modifications may be made under
the teachings of the present disclosure. However, those variations
and modifications do not depart from the scope of the present
disclosure. In some embodiments, the waveform modification module
540 may perform 720 and 730 in any order. For example, the waveform
modification module 540 may perform 720 before or after 730. As
another example, the waveform modification module 540 may perform
720 and 730 simultaneously.
FIG. 8 is a flowchart illustrating an exemplary process for
determining a modified time-domain waveform according to some
embodiments of the present disclosure. The process 800 may be
implemented in the MRI system 100 illustrated in FIG. 1. For
example, the process 800 may be stored in the storage device 150
and/or the storage 320 in the form of instructions (e.g., an
application), and invoked and/or executed by the processing device
140 (e.g., the processor 310 illustrated in FIG. 3, or one or more
modules in the processing device 140 illustrated in FIG. 5). The
operations of the illustrated process presented below are intended
to be illustrative. In some embodiments, the process 800 may be
accomplished with one or more additional operations not described,
and/or without one or more of the operations discussed.
Additionally, the order in which the operations of the process 800
as illustrated in FIG. 8 and described below is not intended to be
limiting. In some embodiments, operation 640 illustrated in FIG. 6
may be performed according to the process 800.
In some embodiments, the waveform modification module 540 may
repeatedly update the corrected time-domain determined in 640 of
FIG. 6 in an iteration process including a plurality of iterations
(e.g., each iteration may include operations 810-840), until
satisfying a termination criterion. For instance, an iteration
process including one or more iterations (e.g., each iteration may
include operations 810-840) may be performed for determining a
modified time-domain waveform.
In 810, the waveform modification module 540 may determine an
updated time-domain waveform based on the designed time-domain
waveform and a previous output time-domain waveform. The previous
output time-domain waveform may correspond to an output RF pulse
generated by the RFPA 207 based on the designed time-domain
waveform in a first iteration or an output RF pulse generated by
the RFPA 207 based on a previously updated time-domain waveform
determined in a previous iteration. In some embodiments, the
waveform modification module 540 may determine the updated
time-domain waveform based on the process 700 described in FIG.
7.
For example, the waveform modification module 540 may transform the
previous output time-domain waveform into a previous output
frequency-domain waveform. The waveform modification module 540 may
determine one or more sidebands (also referred to as
frequency-domain sidebands) in the previous output frequency-domain
waveform by comparing the designed frequency-domain waveform with
the previous output frequency-domain waveform. The waveform
modification module 540 may select a portion (e.g., 1130 and/or
1140 in FIG. 11) of the previous output frequency-domain waveform.
The waveform modification module 540 may determine a compensation
frequency-domain waveform based on the selected portion. A phase
difference between the compensation frequency-domain waveform and
the selected portion may be 180.degree.. The waveform modification
module 540 may determine the compensation frequency-domain waveform
by reversing the phase of the selected portion of the previous
output frequency-domain waveform. The waveform modification module
540 may transform the compensation frequency-domain waveform into a
compensation time-domain waveform. The waveform modification module
540 may determine an updated time-domain waveform based on the
compensation time-domain waveform and the previous output
time-domain waveform.
In 820, the control module 520 may direct the RFPA 207 to generate
an updated output RF pulse based on the updated time-domain
waveform. In some embodiments, the control module 520 may direct
the waveform generator 216 to generate an input RF pulse based on
the updated time-domain waveform, and direct the waveform generator
216 to transmit output signals of the generated input RF pulse to
the RFPA 207. The control module 520 may direct the RFPA 207 to
amplify the input RF pulse (e.g., the power of the input RF pulse,
the voltage of the input RF pulse) and generate an updated output
RF pulse.
In 830, the output pulse acquisition module 530 may measure an
output time-domain waveform of the updated output RF pulse. The
updated output RF pulse generated by the RFPA 207 may be sent to
the ADC 208. The ADC 208 may transform analog signals of the
updated output RF pulse into digital signals of the updated output
RF pulse. The digital signals of the updated output RF pulse may be
sent to the output pulse acquisition module 530. The output pulse
acquisition module 530 may collect the signals of the updated
output RF pulse and measure the output time-domain waveform based
on the collected signals of the updated output RF pulse.
In 840, the waveform modification module 540 may determine whether
a termination criterion is satisfied. In some embodiments, the
termination criterion may relate to a desired iteration count, a
desired output RF pulse, a desired (time-domain or
frequency-domain) output waveform, or the like, or a combination
thereof.
Merely by way of example, the termination criterion may relate to a
desired iteration count. The waveform modification module 540 may
determine whether an iteration count of the iterations that have
been performed is equal to or greater than a first threshold (e.g.,
3 iterations). In response to the determination that the iteration
count is equal to or greater than the first threshold, the waveform
modification module 540 may terminate the iteration process, and
the process 800 may proceed to 850. In response to the
determination that the iteration count is lower than the first
threshold, the waveform modification module 540 may initiate a new
iteration, and the process 800 may proceed to 810. The counting of
the iterations that have been performed may be done automatically
by the waveform modification module 540 without user
intervention.
As another example, the termination criterion may relate to a
desired output RF pulse or a desired output (time-domain or
frequency-domain) waveform. In some embodiments, the decision to
terminate the iteration process based on an output RF pulse or
waveform may be performed automatically without user intervention.
For instance, an output (time-domain or frequency-domain) waveform
corresponding to an output RF pulse generated in an iteration may
be analyzed automatically. On the basis of the result of the
analysis, a decision may be made automatically by the waveform
modification module 540 as to whether to termination the iteration
process. In some embodiments, the output (time-domain or
frequency-domain) waveform may be analyzed to determine whether it
contains a sideband whose magnitude exceeds a threshold. The
threshold may be provided by a user or determined by the system
100.
In some embodiments, the decision to terminate the iteration
process based on an output RF pulse or waveform may be performed
with user intervention. For instance, a frequency-domain waveform
of the output RF pulse generated by the RFPA 207 based on the
modified time-domain waveform determined in the current iteration
may be displayed to a user. The user may be prompted or allowed to
provide an instruction related to the modified time-domain waveform
determined in the current iteration. The waveform modification
module 540 may terminate the iteration process or initiate a new
iteration of the iteration process based on the instruction. In
some embodiments, when the waveform modification module 540
receives an instruction indicating that the frequency-domain
waveform (or a difference between the designed frequency-domain
(e.g., the designed frequency-domain described in 720 in FIG. 7)
and the frequency-domain waveform of the output RF pulse generated
by the RFPA 207 based on the modified time-domain waveform
determined in the current iteration) of the output RF pulse
generated by the RFPA 207 based on the modified time-domain
waveform determined in the current iteration is acceptable, the
waveform modification module 540 may terminate the iteration
process. For instance, the user may decide, based on the display,
that the frequency-domain waveform of the output RF pulse generated
by the RFPA 207 based on the modified time-domain waveform
determined in the current iteration is acceptable when no visible
sidebands are present or the magnitudes of all sidebands are lower
than a threshold. When the waveform modification module 540
receives an instruction indicating that the frequency-domain
waveform (or a difference between the designed frequency-domain
(e.g., the designed frequency-domain described in 720 in FIG. 7)
and the frequency-domain waveform of the output RF pulse generated
by the RFPA 207 based on the modified time-domain waveform
determined in the current iteration) of the output RF pulse
generated by the RFPA 207 based on the modified time-domain
waveform determined in the current iteration is unacceptable, the
waveform modification module 540 may initiate a new iteration of
the iteration process.
As a further example, the termination criterion may relate to both
a desired iteration count and a desired output RF pulse or a
desired output (time-domain or frequency-domain) waveform. For
instance, the termination criterion is that a certain number of
iterations have been performed or that a desired output RF pulse or
a desired output (time-domain or frequency-domain) waveform is
obtained, whichever occurs earlier or later. The waveform
modification module 540 may decide whether to termination the
iteration process based on the termination criterion. The decision
to terminate the iteration process based on an output RF pulse or
waveform may be performed automatically without user intervention,
or with user intervention.
In 850, the waveform modification module 540 may designate the
updated time-domain waveform determined in the last iteration of
the iteration process as the modified time-domain waveform
corresponding to the excitation RF pulse.
It should be noted that the above description of the process for
determining the modified time-domain waveform is provided for the
purposes of illustration, and is not intended to limit the scope of
the present disclosure. For persons having ordinary skills in the
art, multiple variations and modifications may be made under the
teachings of the present disclosure. However, those variations and
modifications do not depart from the scope of the present
disclosure.
EXAMPLES
The following examples are provided for illustration purposes and
not intended to limit the scope of the present disclosure.
FIG. 9 shows an exemplary designed time-domain waveform and a
corresponding output time-domain waveform according to some
embodiments of the present disclosure. The output time-domain
waveform may be generated by an RFPA based on the designed
time-domain waveform. A time-domain waveform may be a scanning
sequence illustrating a relationship between the time and the
magnitude/phase of an RF pulse. The horizontal axis is time in
microseconds, and the vertical axis is magnitude (e.g., a relative
value) in arbitrary unit (a.u.). In some embodiments, because of
the hardware infidelity, the designed time-domain waveform and the
output time domain waveform may be different. As shown in FIG. 9,
magnitude 910 of the output time-domain waveform corresponding to a
time point is larger than and/or different from magnitude 920 of
the designed time-domain waveform corresponding to the same time
point.
FIG. 10 shows an exemplary designed frequency-domain waveform
according to some embodiments of the present disclosure. A
frequency-domain waveform may illustrate a relationship between a
frequency and the magnitude/phase of an RF pulse. The horizontal
axis is frequency in kHz, and the vertical axis is magnitude (e.g.,
a relative value) in a.u. The designed frequency-domain waveform
corresponds to the designed time-domain waveform illustrated in
FIG. 9. As shown in FIG. 10, the designed frequency-domain waveform
may include two excitation bands (e.g., peak 1010, peak 1020) used
to excite two slices of an object simultaneously in an excitation
of an MRI scan.
FIG. 11 shows an exemplary output frequency-domain waveform
according to some embodiments of the present disclosure. The
horizontal axis is frequency in kHz, and the vertical axis is
magnitude (e.g., a relative value) in a.u. The output
frequency-domain waveform corresponds to the output time-domain
waveform illustrated in FIG. 9. As shown in FIG. 11, the output
frequency-domain waveform may include two excitation bands (e.g.,
peak 1010, peak 1020) and one or more sidebands (e.g., peak 1102,
peak 1104, peak 1106, peak 1108). In some embodiments, the waveform
modification module 540 may determine the one or more sidebands by
comparing the designed frequency-domain waveform in FIG. 10 with
the output frequency-domain waveform in FIG. 11. The waveform
modification module 540 may determine the one or more sidebands by
selecting, for example, section 1130 and/or section 1140 of the
output frequency-domain waveform. Section 1130 and section 1140 may
include the one or more sidebands (e.g., peak 1102, peak 1104, peak
1106, peak 1108) but not the two excitation bands (e.g., peak 1010,
peak 1020).
FIG. 12 shows an exemplary corrected output frequency-domain
waveform according to some embodiments of the present disclosure. A
modified time-domain waveform may be determined by modifying the
designed time-domain waveform illustrated in FIG. 9 using the
methods (e.g., the process 600 illustrated in FIG. 6, the process
700 illustrated in FIG. 7, the process 800 illustrated in FIG. 8)
described in the disclosure. The corrected output frequency-domain
waveform may correspond to an output RF pulse generated by the RFPA
207 in FIG. 2 based on the modified time-domain waveform. As shown
in FIG. 12, compared to the output frequency-domain waveform in
FIG. 11 and the designed frequency-domain waveform in FIG. 10,
sidebands in the corrected output frequency-domain waveform were
reduced.
FIG. 13 is a schematic diagram illustrating an exemplary
simultaneous multi-slice (SMS) imaging according to some
embodiments of the present disclosure. Methods and systems
described in the disclosure may be applied to SMS imaging. In SMS
imaging, two or more slices may be excited simultaneously by an
excitation RF pulse in an excitation. Merely by way of example, as
shown in FIG. 13, N slices of an object need to be excited in an
MRI scan. In one excitation, two slices may be excited
simultaneously by an excitation pulse including two excitation
bands. For example, in excitation A, slice 1 and slice N/2+1 may be
excited simultaneously by a first excitation RF pulse. As another
example, in excitation B, slice 2 and slice N/2+2 may be excited
simultaneously by a second excitation RF pulse. As still another
example, in excitation C, slice 3 and slice N/2+3 may be excited
simultaneously by a third excitation RF pulse. Excitation A,
excitation B, and excitation C may be performed one by one.
Accordingly, the scan time may be halved compared to the way of
exciting one slice in an excitation.
FIG. 14 is a schematic diagram illustrating exemplary image
reconstruction in SMS imaging according to some embodiments of the
present disclosure. As shown in FIG. 14, image 1410 includes
aliasing artifacts related to two slices excited simultaneously in
an excitation in SMS imaging. Multiple receiving coils with
sufficient spatial encoding capabilities were used to separate the
overlapping slices in image 1410. Image signals that were aliased
into one pixel were separated by exploiting the sensitivity
information inherent to the receiving coils. Exemplary
reconstruction techniques may include sensitivity encoding (SENSE),
Gene Relized Autocalibrating Partially Parallel Acquisitions
(GRAPPA), or the like, or any combination thereof. Image 1420 shows
a single slice separated from image 1410. Image 1430 shows a single
slice separated from image 1410.
Having thus described the basic concepts, it may be rather apparent
to those skilled in the art after reading this detailed disclosure
that the foregoing detailed disclosure is intended to be presented
by way of example only and is not limiting. Various alterations,
improvements, and modifications may occur and are intended to those
skilled in the art, though not expressly stated herein. These
alterations, improvements, and modifications are intended to be
suggested by this disclosure, and are within the spirit and scope
of the exemplary embodiments of this disclosure.
Moreover, certain terminology has been used to describe embodiments
of the present disclosure. For example, the terms "one embodiment,"
"an embodiment," and/or "some embodiments" mean that a particular
feature, structure or characteristic described in connection with
the embodiment is included in at least one embodiment of the
present disclosure. Therefore, it is emphasized and should be
appreciated that two or more references to "an embodiment" or "one
embodiment" or "an alternative embodiment" in various portions of
this specification are not necessarily all referring to the same
embodiment. Furthermore, the particular features, structures or
characteristics may be combined as suitable in one or more
embodiments of the present disclosure.
Further, it will be appreciated by one skilled in the art, aspects
of the present disclosure may be illustrated and described herein
in any of a number of patentable classes or context including any
new and useful process, machine, manufacture, or composition of
matter, or any new and useful improvement thereof. Accordingly,
aspects of the present disclosure may be implemented entirely
hardware, entirely software (including firmware, resident software,
micro-code, etc.) or combining software and hardware implementation
that may all generally be referred to herein as a "unit," "module,"
or "system." Furthermore, aspects of the present disclosure may
take the form of a computer program product embodied in one or more
computer readable media having computer readable program code
embodied thereon.
A non-transitory computer readable signal medium may include a
propagated data signal with computer readable program code embodied
therein, for example, in baseband or as part of a carrier wave.
Such a propagated signal may take any of a variety of forms,
including electro-magnetic, optical, or the like, or any suitable
combination thereof. A computer readable signal medium may be any
computer readable medium that is not a computer readable storage
medium and that may communicate, propagate, or transport a program
for use by or in connection with an instruction execution system,
apparatus, or device. Program code embodied on a computer readable
signal medium may be transmitted using any appropriate medium,
including wireless, wireline, optical fiber cable, RF, or the like,
or any suitable combination of the foregoing.
Computer program code for carrying out operations for aspects of
the present disclosure may be written in any combination of one or
more programming languages, including an object oriented
programming language such as Java, Scala, Smalltalk, Eiffel, JADE,
Emerald, C++, C #, VB. NET, Python or the like, conventional
procedural programming languages, such as the "C" programming
language, Visual Basic, Fortran 2003, Perl, COBOL 2002, PHP, ABAP,
dynamic programming languages such as Python, Ruby and Groovy, or
other programming languages. The program code may execute entirely
on the user's computer, partly on the user's computer, as a
stand-alone software package, partly on the user's computer and
partly on a remote computer or entirely on the remote computer or
server. In the latter scenario, the remote computer may be
connected to the user's computer through any type of network,
including a local area network (LAN) or a wide area network (WAN),
or the connection may be made to an external computer (for example,
through the Internet using an Internet Service Provider) or in a
cloud computing environment or offered as a service such as a
Software as a Service (SaaS).
Furthermore, the recited order of processing elements or sequences,
or the use of numbers, letters, or other designations therefore, is
not intended to limit the claimed processes and methods to any
order except as may be specified in the claims. Although the above
disclosure discusses through various examples what is currently
considered to be a variety of useful embodiments of the disclosure,
it is to be understood that such detail is solely for that purpose,
and that the appended claims are not limited to the disclosed
embodiments, but, on the contrary, are intended to cover
modifications and equivalent arrangements that are within the
spirit and scope of the disclosed embodiments. For example,
although the implementation of various components described above
may be embodied in a hardware device, it may also be implemented as
a software only solution, e.g., an installation on an existing
server or mobile device.
Similarly, it should be appreciated that in the foregoing
description of embodiments of the present disclosure, various
features are sometimes grouped together in a single embodiment,
figure, or description thereof for the purpose of streamlining the
disclosure aiding in the understanding of one or more of the
various inventive embodiments. This method of disclosure, however,
is not to be interpreted as reflecting an intention that the
claimed subject matter requires more features than are expressly
recited in each claim. Rather, inventive embodiments lie in less
than all features of a single foregoing disclosed embodiment.
In some embodiments, the numbers expressing quantities, properties,
and so forth, used to describe and claim certain embodiments of the
application are to be understood as being modified in some
instances by the term "about," "approximate," or "substantially."
For example, "about," "approximate," or "substantially" may
indicate .+-.20% variation of the value it describes, unless
otherwise stated. Accordingly, in some embodiments, the numerical
parameters set forth in the written description and attached claims
are approximations that may vary depending upon the desired
properties sought to be obtained by a particular embodiment. In
some embodiments, the numerical parameters should be construed in
light of the number of reported significant digits and by applying
ordinary rounding techniques. Notwithstanding that the numerical
ranges and parameters setting forth the broad scope of some
embodiments of the application are approximations, the numerical
values set forth in the specific examples are reported as precisely
as practicable.
Each of the patents, patent applications, publications of patent
applications, and other material, such as articles, books,
specifications, publications, documents, things, and/or the like,
referenced herein is hereby incorporated herein by this reference
in its entirety for all purposes, excepting any prosecution file
history associated with same, any of same that is inconsistent with
or in conflict with the present document, or any of same that may
have a limiting affect as to the broadest scope of the claims now
or later associated with the present document. By way of example,
should there be any inconsistency or conflict between the
description, definition, and/or the use of a term associated with
any of the incorporated material and that associated with the
present document, the description, definition, and/or the use of
the term in the present document shall prevail.
In closing, it is to be understood that the embodiments of the
application disclosed herein are illustrative of the principles of
the embodiments of the application. Other modifications that may be
employed may be within the scope of the application. Thus, by way
of example, but not of limitation, alternative configurations of
the embodiments of the application may be utilized in accordance
with the teachings herein. Accordingly, embodiments of the present
application are not limited to that precisely as shown and
described.
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